There is now scientific consensus that the incidence of neural tube defects can be reduced by intakes of folic acid of 0.4 mg per day. A 1991 clinical trial focused on prevention of recurrent neural tube defects, ie, in women who have already given birth to an affected child. More recently, Werler et al1 conducted a multicenter case-control study, the object of which was to determine whether periconceptual supplementation with folic acid would reduce the first occurrence of neural tube defects. The investigators found that there was a dose-related decline in the occurrence of neural tube defects, which was inversely related to the mother's folate intake. Moreover, those who took daily dietary supplements containing 0.4 mg of folic acid during the periconceptual period had a significantly lower relative risk of having a baby with a neural tube defect. Although the present recommended dietary allowance (RDA) for folic acid is